In the formation of a cable from a number of conductors, it is beneficial to twist the conductors about the axis of the cable. Besides maintaining the conductors assembled, this increases the flexibility of the cable. Additionally, in the case of electrical conductors, the twisting reduces cross talk among the various circuits in which the conductors are employed.
One method of twisting the conductors involves continuously twisting the conductors in the same direction as the cable advances. This method requires the use of a planetary cabler which continuously rotates the conductor supply spools about the direction of travel of the cable. Such planetary cablers are large, complex and very expensive. Additionally, they must be stopped periodically to replace the exhausted conductor spools.
In an SZ cable, the conductors are twisted in a clockwise direction for a number of turns, and then the conductors are twisted in a counterclockwise direction for a like number of turns before again reversing the twist direction. While an SZ twist does result in spaced transition positions (where the twist direction is changed) and does require that a wrap or outer jacket be provided to hold the conductors from untwisting, an SZ twist can be fabricated with relatively simple equipment. Conventional SZ cablers employ an accumulator tube, for accumulating turns of the conductors on its outside surface, which rotates in one direction and then reverses after a predetermined number of turns. However, relatively few turns can be accumulated on the tube before the direction must be reversed. Otherwise the frictional engagement between the conductors and the tube becomes too great, resulting in damage to the conductors.
One proposed SZ cabler includes an accumulator tube which is reciprocated in the direction of travel of the cable by means of a reversible motor. A second reversible motor is provided which rotates the accumulator tube, an intermediate guide ring and a downstream guide ring. This apparatus requires that the number of turns of the conductor on the tube be counted and that, upon a predetermined number of turns being achieved, the direction of rotation is reversed. For further information regarding the structure and operation of this relatively complex SZ cabler, reference may be made to U.S. Pat. No. 4,586,327.